Process of preparing dibenzyl



Patented Mar 14, 1944 PROCESS OF PREPARING DIBENZYL Robert H. Van Schaack, Jr., Evanston, 111.

No Drawing. Application February 18, 1942.

' Serial No. 431,381

Claims.

This invention relates to a process of preparing dibenzyl and more particularly to a process by which may be obtained much higher yields of dibenzyl than has been heretofore possible.

The preparation of dibenzyl by a Friedel-Craits reaction has been known. However, this reaction as heretofore practiced in the art, has produced relatively small yields of dibenzyl and has normally produced from to 40 per cent of high boiling by-products which it has been necessary to discard. Because of the poor yields normally resulting from this process as used in the art, other methods have usually been preferred for the preparation of dibenzyl, for instance, the preparation of dibenzyl from benzyl chloride.

When benzol is reacted with ethylene dichloride in the presence of aluminum chloride in accordance with standard Friedel-Craits conditions to form dibenzyl, certain by-products are produced which boil at a temperature higher than the boiling point of dibenzyl. These by-produots form a residue which may vary in quantity between i 20 and 40 per cent of the combined weight of the dibenzyl and the residue, and have heretofore been found to serve no useful purpose. The yield of dibenzyl, therefore, is normally not greater than 80 per cent and will usually be less than this amount.

With my improved process, the yield of dibenzyl produced from the reaction of benzol and ethylene dichloride may be reatly increased and may even closely approach 100 per cent. The process contemplates the reaction of ethylene dichloride with an excess of benzol in the presence of a Friedel-Crai'ts catalyst and with a substantial portion of a high boiling residue of a previous reaction between benzol and ethylene dichloride. Inorder to use my process, dibenzyl may first be prepared by a Friedel-Craits reaction, using ethylene dichloride and an excess of benzol in the presence of anhydrous aluminum chloride. If desired, the cost oi the process may be decreased without aflecting the efficiency of the reaction by substituting aluminum metal, previously struck with a thin copper plate, together with a small amount of anhydrous aluminum chloride for the relatively large quantity of anhydrous aluminum chloride which would otherwise be used.

The following is an example of the preparation of dibenzyl following the standard or normal Friedel-Crafts conditions but using metallic aluminum as above mentioned. Six hundred twenty-four grams of anhydrous benzol and 10 grams or flnely ground aluminum which have been struck with copper were placed in a threenecked boiling flask equipped with a thermometer and a reflux condenser. The flask was then heated until the benzol was refluxing. Six hundred twenty-four grams oi anhydrous benzol were thoroughly mixed with 198 grams of anhydrous ethylene dichloride and placed in a dropping funnel attached to the flask. Approximately gram of anhydrous aluminum chloride was then added to the mixture in the flask to start the reaction. The mixture in the dropping funnel was then run into the boiling flask at a uniform rate, taking approximately three hours to deliver the entire quantity to the flask. After the entire mixture was received within the flask, the batch was refluxed for approximately one hour. Throughout the operation the flask was heated and the mixture therein maintained a temperature of between 82 C. and 87 C.

The reaction product was washed with water, filtered and the unreacted benzol distilled off. The product was then distilled in a vacuum of approximately 14 mm. pressure up to a temperature of approximately 0.. at which point substantially all of the dibenzyl had been removed. 233.2 grams of dibenzyl were separated by the distillation while 80.7 grams of residue remained in the flask. Thus the residue remaining in the flask comprised 25.3 per cent oi the combined weight of the residue and the dibenzyi.

In my preferred method of preparing dibenzyl, the residue obtained from this reaction of benzol and ethylene dichloride is added to a new reaca mixed with 198 grams or ethylene dichloride and slowly added to a mixture consisting oi the 80.7 grams of the high boiling residue obtained from the reaction described above and 624 grams of benzol, and were treated in the manner described above in connection with the previous example. After the reaction was complete the product was washed, flltered, and distilled to remove unreacted benzol. The dibenzyl was then distilled oil. The quantity oi dibenzyl obtained from this reaction was 285.6 grams. 119.3 grams of residue remained in the flask. Since 80.7 grams of residue remained in the flask from the previous reaction, the residue formed by this reaction was only 38.6 grams or 11.9 per cent of the combined weight at the dibenzyl and residue formed in this reaction.

I have found that by permitting the men ton in: residue to remain in the reaction chamber throughout a large number reactions, the

quantity oi high boiling residue is reduced to a minimum. For example, im a series oi twelve reactions treated in the manner above described, 3552.! grams 0! dibenzyl were prepared while only 106.5 grams of the high boiling residuewere produced. Y

I have iolmd that it is desirable to add to the reaction mixture the entire mixture oi by-prod-' ucts or high boiling residue obtained from the previous reaction. These 'by-prorlucts have not been isolated or identified. It seems certain, how-- V ever, that the residue contains a mixture oi several substances, since viractional distillation oi the mixture produces a limited separation oi the I convert at least a substantial portion oi the same into dibenzyl. In order to carry out such conversion, it is necessary only to react the hish boiling residue with an excess oi benzol in the presence oi aluminum chloride. 1

For example, 50 grams of high boiling residue obtained from the reaction oi benzol and ethylene dichloride were refluxed with 250 grams of products. Moreover, the residue contains a mix-.

ture oi liquids and solids, some oi them being inv the irom oi tar-like substances.

, Although in the specific examples above de. scribed approximately 8 mols oi benzol were used benzol and 5 grams of anhydrous aluminum chloride. This high boiling residue was substantially iree oi ethylene dichloride. The temperature was maintained at approximately 82' C. After 5% hours the mixture was cooled,

'washed with-water and the benzol distilled oil. The balanceoi' the productwas distilled in a vacuum; oi. 14 mm. up to a temperature oi approximately 175 tonremove therefrom practipally all of the dibenzyl. It is iound that this to each mol oi ethylene dichloride, it is, nevertheg less, possible to vary this ratio considerably withoutgreatly aiiecting the reaction products. At

least two mols oi benzol should, however, be used with each mol oi ethylene dichloride in order to siderable excess oi benml since the use oi such an excess appears to be important in maintaim' ing at a minimum the quantity oi high boiling" residue which is produced. By anexcess oi bena 1 sol I mean' a quantity oi benzol greater than that required ior molecular proportions oi the re- I obtain a reaction oi all or the ethylene d1Ch10-, I ride. Furthermore, it is desirable to use a con- 1 reaction produced grams oi dibenzyl and that only approximately 15 grams oi the highboiling residue remained unconverted.

While the first method abovedeserlbed is to be, preferred, the method oi converting the high boiling residue into dibenzyl is also very ei'iective to increase the yield of this product,-

.In carrying out the reaction between benzol and ethylene dichloride, substantial quantities oi 1 aluminum chloride are used. The cost oi the Y? 1 reaction may be greatly decreased byusing inactants or more than two mols oi benzol ior each mol oi ethylene dichloride. 7 The quantities oi the high boiling residue which may be added to the reaction mixture may varied considerably without seriously ail'ectlng the emciency oi the operation. Thus,

I preier to use high boiling residue in an amount equal to approximately percent by weight of the amount oi ethylene dichloride used, quanti-[j 4 ties varying irom 25 to '75 per cent oi the weight '1; oi ethylene dichloride may be used with bene- The reason ior the action or this high boilins ncial results.

residue in inhibiting the formation of additional residue is not iully understood. It may be that the reaction-is aflected bythe iormationoi acomplex equilibrium. Thus it would be possible tor the presence oi the high boiling residue to shiit the equilibrium away irom the formation oi more residue and tend to increase the yieldoi dibenzyl produced. Moreover, the use oi an excess oi benzol may not only aid in iormingthe maximum quantities of dibcnzyl but may cause the high boiling residue iormed in the course 01 the reaction to react with the benzol to 10m additionai quantities oi dibenzyfi However, I do not wlshtostatethatthisisthemechanismoithe reaction and do not wish tobe bound by any specified theory.

Since the composition and structure ,oi by-products obtained irom this-motion a're niit known. I have reierred to the mixture as a high boiling residue oi a reaction between benzol. and

stead oia large quantity of aluminum chloride ji only a very small quantity oi this reagent with metallic aluminum. It appears that once 1 reaction is started by the aluminum chloride,-.

the metallic aluminum serves to continue the catalysis, and the eillciency oi the reaction is. l I not aiiected. It is probable that the hydrochloric acid iormed in the reaction converts the metailic aluminum to aluminum chloride. For this purpose, auy suitable amount oi metallic alumi-' nunr may be used,preierably' in the neighbor hood oi irom to l 'to 10 per cent oi the weight".

oi ethylene dichloride used. In this connection,

it should be understood that the aluminum need not be pure and that, in iact,'impure aluminum has actually been iound to be even more eflective thanthepuremetal.

. The'eiiiciency oi-the metallic aluminum may actually be increased by at least partially coating it with a very thingcopper plate. This may be done by merely dipping the aluminum in a water solution 0! a copper salt. The copper salt solution causes metallic copper to be deposited on the surface oi the aluminum. The copper plated aluminum is dried and is then ready ior use. The resulting product, which is known as aluminum struck with copper, may be used in place oi the pure aluminum and is hizhly eflece tive in the above reaction. Although the reason for this action oi the copper and aluminum is not known, it is believed that the electrolytic eflect oi the contact oi the two metals serves to increase their catalytic action.

Although the reaction may be carried out in the presence oi anhydrous aluminum chloride,

any other suitable catalyst may be used. Any

ot the other catalysts which are known for use in Friedei-Craits reactions may be used. As

by merely treating' the high boiling residue to stated above, metallic aluminum in the presence oi a very small quantity oi aluminum chloride provides an eflective catalyst.

nickel, iron, boron, tin, zinc, antimony and cadmium may be used. Catalysts oi this type including all oi the specific catalysts named are Similarly, such catalysts as the halides of chromium manganese.

referred to herein for convenience as Friedeh Crafts catalysts.

This application is a continuationdn-part oi my co-pending application Serial No. Ziilfidl, filed October 2, 1939.

The foregoing specific examples have given for the purpose of illustrating the insert tion and means practicing it. @hanges and modifications may therefore he made in the process as set forth, particularly as to quantities of the reagents used and as to the conditions of the reactions without departing from the spirit and scope of my invention.

I claim:

- 1. A process of preparing dibenzyl which comprises mixing benzol with ethylene dichloride in the presence of a Friedel-Craits catalyst and the high boiling residue of a previous reaction he-= tween benzol and ethylene dichloride, said resi due being soluble in the reaction mixture and heating the mixture.

2. A process of preparing dibenzyl which comprises mixing ethylene dichloride with an excess of benzol in the presence of a Fricdel-Craits catelyst and the high boiling residue of a previous reaction between benzol and ethylene dichloride, said residue being soluble in the reaction mixture and heating the mixture.

3. A process as set forth in claim 2, wherein the weight of the high boiling residue is between 25% and 75% of the weight of the ethylene cli= chloride.

4. A process of preparing dibenzyl which corn prises slowly mixing benzol with ethylene dichlo ride according to the ratio of approximately 3 mole of benzol to each mol of ethylene dichloride in the presence of a Frledel-Crafts catalyst and the high boiling residue of a reaction between benzol and ethylene dichloride, said residue being soluble in the reaction mixture and heating the mixture to complete. the reaction;

5. A process of preparing dibenzyl which comprises slowly mixing benzol with ethylene dichlo ride according to the ratio of approximately 8 mols oi benzol to each moi of ethylene dichloride, in the presence of anhydrous aluminum chloride, metallic aluminum, and the high boiling residue oi the reaction between benzol and ethylene di chloride, said residue being soluble in the reaction mixture, the aluminum chloride, aluminum and high boiling residue being present in amounts equal to approximately 0.1%, 5% and by weight respectively of the quantity of ethylene dichloride used, and heating the mixture to compiste the reaction.

6. A process of preparing dibenzyl which comprises reacting an excess of benzol with ethylene dichloride in the presence of a small quantity 01 a Friedel-Qrafts catalyst, washing the reaction products with water, distilling the reaction prodnets to remove unreacted benzol, further distilling the reaction products to remove dibenzyl, and reacting the high boiling residue with ethylene dichloride and an excess of benzol in the absence of water and in the presence of a Friedel-Craits catalyst.

7. A process oi preparing dlbenzyl which comprises treating metallic'aluminum with a water solution of a copper salt, drying the aluminum product, adding the same to a mixture of ethylene dichloride and an excess of benzol and a very small quantity of anhydrous aluminum chloride, and heating the resulting mixture.

8. A process of preparing dibenzyl which comprises reacting the high boillng residue of a reaction between benzol and ethylene dichloride, said residue being free of ethylene dichloride, with benzol in the presence of a Friedel-Crafts catalyst.

9. A process of preparing dihenzyl which comprises reacting one part by weight of the high boiling residue of a reaction between benzol and ethylene dichloride, said residue being free of ethylene dichloride with approximately five parts of benzol in the presence of a small quantity of aluminum chloride.

it. A process of preparing dibenzyl which comprises reacting an excess of benzol with ethylene dichloride in the presence of aluminum chloride and the high boiling residue of a reaction between henaol and ethylene dichloride, distilling oh the unreacted benzol, distilling in vacuum to obtain the dibenzyl, and reacting the high boiling residue with benzol and anhydrous aluminum chloride to produce additional dibenzyl.

ROBERT H. VAN SCI-IAACK, JR. 

